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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

2IO

ELECTROLYTIC ANALYSIS OF METALS

FIG. 17

size. For analysis with stationary electrodes, a battery of 4 elements of
30-50 ampere-hour capacity is sufficient, whilst rotating electrodes may
require 12 accumulators of this capacity. The various elements should
connect with either a mercury or plug commutator, so that they may be
grouped readily in parallel or in series or in mixed formation according to

circumstances.

The electricity supply current may also be used and, if continuous, requires

only the insertion of suitable resist-
ances. If alternating, it must be con-
verted into continuous current by an
electrolytic rectifier, which serves par-
ticularly well when only low current
intensities are required (1-1-5 amp.).

Fig. 16 shows an electrolytic rec-
tifier in connection with a small
switchboard and the other arrange-
ments necessary for electrolytic
analysis.

2, Distribution of the Current.
—The switchboard for distributing
the current is very simple. It includes
essentially a rheostat (Fig. 17, R) to
regulate the current, an accurate amperemeter and voltmeter, a commu-
tator C for inserting or cutting-out the amperemeter in the circuit including
the electrolytic cell, and an interrupter B to insert at will the voltmeter
and measure the pressure at the terminals. In any laboratory the current
may be distributed in the form most convenient to the particular circum-
stances.

3. Electrodes and Supports.—In general the electrodes are of plati-
num or iridised platinum and
that on which the metal is de-
posited, that is, the cathode, is
of greater surface than the
anode.

(a) WITH STATIONARY ELEC-
TRODES. Electrodes. Of the
numerous electrodes of different
form and dimensions which have
been suggested, those most suit-
able in practice are :

The   Classen   dish,   with    a

smooth or matte surface (Fig. 18, a). This is a platinum dish of slightly
convex base, weighing about 40 grams, holding about 200 c.c. and con-
stituting the cathode. The anode is a disc of about 4-5 cm. in diameter
with 5 holes, and supported by a stout platinum wire (Fig. 18, c) ;
instead of this, a horizontal wire spiral may be used (Fig. 18, 6).

Winkler's gauze electrodes.   These are generally preferred because they
weigh little (14-15 grams), permit perfect mixing of the liquid, are readily

FIG. 18.e coloration